President Donald Trump said on Tuesday that his administration will end an Obama-era program that offers some protection to thousands of young undocumented immigrants brought to the United States as children. But he will give lawmakers six months to act first, effectively punting the fate of so-called Dreamers into the hands of Congress.

It’s not clear whether Republican lawmakers, who have struggled for years to agree on an immigration reform package and who face a series of other high-stakes deadlines this fall, will be able to score a legislative solution by March.

But the countdown clock began ticking Tuesday morning.

“It is now time for Congress to act!” Trump declared in a lengthy statement.

The president said the Department of Homeland Security will start “an orderly transition and wind-down” of former President Barack Obama’s Deferred Action for Childhood Arrivals program — “with minimum disruption.”

“This is a gradual process, not a sudden phase out. Permits will not begin to expire for another six months, and will remain active for up to 24 months,” Trump said. “Thus, in effect, I am not going to just cut DACA off, but rather provide a window of opportunity for Congress to finally act.”

House Speaker Paul Ryan, who last Friday called on Trump to not immediately end DACA, on Tuesday called the program “a clear abuse of executive authority" while encouraging lawmakers to act quickly on the issue.

“It is my hope that the House and Senate, with the president's leadership, will be able to find consensus on a permanent legislative solution that includes ensuring that those who have done nothing wrong can still contribute as a valued part of this great country,” Ryan (R-Wis.) said in a statement.

But there are deep divisions among Republicans about how to tackle the issue, and some lawmakers tried to put the pressure back on the White House.

Sen. Marco Rubio (R-Fla.), a member of the failed Gang of Eight immigration reform effort in 2013, said: “It is important that the White House clearly outline what kind of legislation the president is willing to sign. We have no time to waste on ideas that do not have the votes to pass or that the president won’t sign.”

Trump has wrestled for months with how to handle the future of DACA, which many Republicans consider a major executive overreach by Obama. While the president promised on the campaign trail to end the program, he has repeatedly expressed sympathy for the roughly 800,000 young immigrants who were brought to the U.S. as children and have received work permits under the program.

“I do not favor punishing children, most of whom are now adults, for the actions of their parents,” Trump said Tuesday. “But we must also recognize that we are nation of opportunity because we are a nation of laws.”

Acting Homeland Security Secretary Elaine Duke on Tuesday formally rescinded the memo that created DACA in 2012, as Attorney General Jeff Sessions offered a lengthy legal justification for the decision. Sessions outlined his concerns with the DACA program in a letter on Monday, according to one senior DHS official. And the attorney general said he advised the president and DHS to begin “an orderly, lawful wind-down” of the program.

“This will enable DHS to conduct an orderly change and fulfill the desire of this administration to create a time period for Congress to act — should it so choose. We firmly believe this is the responsible path,” Sessions said, encouraging lawmakers to “carefully and thoughtfully” pursue immigration reform.

Sessions, who briefed the media at the Justice Department on Tuesday, departed without responding to questions shouted by reporters, including about what the government plans to do with information applicants to the DACA program submitted, and whether the administration will target so-called Dreamers for deportation.

A senior DHS official said Dreamers whose work permits expire by March 5 will be allowed to apply for a two-year renewal, as debate continues about the future of the program. The renewal application must be submitted by Oct. 5, and Tuesday is the last day the administration will consider new applications, the official said.

The unclear future of DACA leaves thousands of Dreamers in limbo. More than 10,000 new applications for legal status were filed between January and March (and more than 141,000 renewals were filed within the same time span), according to data provided by the Department of Homeland Security.

Sessions cautioned that the U.S. “must set and enforce” the number of immigrants it admits each year, as he laid out a long legal rationale for the decision. “And that means all cannot be accepted,” he said. “This does not mean they are bad people or that our nation disrespects or demeans them in any way. It means we are properly enforcing our laws as Congress has passed them.”

On a call with reporters Tuesday, senior DHS officials faced repeated questions about whether the information supplied in DACA applications could be used for future deportation efforts.